Breast Size During Pregnancy
Some women get significantly bigger breasts during pregnancy—two or more cup sizes—and some women don't. But in general, your most rapid breast gain occurs in your first trimester, with a break in the second and growth spurt again in the third.
You may not notice a large increase in your size until after your breast milk comes in. This lasts for about a week or two, and then your breasts usually return to the size you were in pregnancy.